First you need to check theme is applied or not. You can check your current theme by ctr + U, you can see current theme path in .css and .js file.
In your case Magestore/Sample display in .css and .js file path. If display it, theme is set properly.
Run below command
php bin/magento setup:upgrade php bin/magento setup:static-content:deploy php bin/magento cache:clean
Now you can see your changes.
Let me know if you have any query.